Dynamic rheological properties of spotted mangrove/high-density polyethylene composites

Abstract

This study describes the viscoelastic characterizations of unmodified and heat-modified mangrove particle (MP)-filled high-density polyethylene (HDPE) composites. The untreated (unmodified) and treated (modified) MPs were compounded with HDPE matrix at 10, 20 and 30 wt% in a twin-screw extruder and compression moulded into thin sheets for rheological characterizations (amplitude and frequency sweeps). The amplitude sweeps of the dynamic rheological analysis indicated that 20 wt% treated composite has the highest linear viscoelastic region of 0.1% with the highest storage and loss modulus of 1310 and 150 kPa, respectively. The frequency sweep showed an increase in storage and loss moduli as particle loading increased. The zero shear viscosities of pure HDPE were nearly 3990 Pa·s, while the MP-reinforced HDPE composites were ≥185,440 Pa·s with treated composites exhibiting higher values.

A Review of Wood Polymer Composites Rheology and Its Implications for Processing

“…On the other hand, at the typical testing temperatures, both dynamic moduli increase with frequency, and, since the storage modulus increases faster than the loss modulus, at a certain frequency a cross-over is reached ( Figure 1 a). This means that the material changes its behavior, i.e., it switches from that of a viscoelastic fluid at low frequencies to that of a viscoelastic solid at higher frequencies [ 14 , 18 , 55 , 72 , 77 , 78 , 79 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 ]. The complex viscosity has a decreasing trend with frequency, similar to a shear thinning fluid, if the Cox-Merz rule was supposed to hold ( Figure 1 b, curve A).…”

“…Like in the case of pressure-driven viscometers, the wood flour content has a great influence on the rheological behavior of WPCs. The storage modulus increases with the wood percentage and so does the loss modulus and the complex viscosity [ 13 , 55 , 65 , 72 , 83 , 86 , 87 , 93 , 94 ]. This behavior is primarily a consequence of the filler-filler and filler-polymer interactions as described previously.…”

“…Some researchers have evaluated the effect of pretreatments on the wood fibers before the compounding phase. Typically, the treatments can be either chemical [ 69 , 77 ] or thermal [ 55 , 83 ], but both aim at modifying the fiber surface and improving the bonding mechanism between matrix and reinforcement. A widely used chemical treatment is the alkaline treatment [ 17 , 19 , 71 , 77 ], which reduces the content of lignin and hemicellulose, making the surface of the fiber rougher and increasing the number of reactive hydroxyl groups [ 71 ].…”

“…Thermal treatments consist in a heating phase that can take place either in boiling water or in inert atmosphere (e.g., nitrogen or argon) and often work by cracking or modifying lignin and hemicellulose. The generalization of these results is not easy because they can influence the complex viscosity in different ways: complex viscosity can increase with thermal treatments [ 83 , 97 ] but may also decrease [ 55 ].…”

“…As for the data obtained with pressure-driven viscometers, the presence of a yield stress is controversial [ 54 , 91 ]. Complex viscosity can also be interpreted with a Carreau-Yasuda equation (12) if a plateau at low frequencies is visible, obtaining a zero shear viscosity that is strongly dependent on the wood content [ 13 , 35 , 83 ] or on the number or reprocessing cycles sustained by the WPCs [ 99 ].…”